RTSP? Isn't that a RealPlayer protocol?
Yeh. I think I've seen it on mobile youtube on a windows mobile 7.5 phone before. In IE on the site, youtube videos would be rtsp links that would be played by something on the phone somehow (since that IE didn't support anything else for playing videos).
I guess in the case of Opera, it might not be getting the right code on the mobile version of youtube. A user-agent switcher might be needed to fool the site. Or, maybe there's an issue with flash in Opera. Maybe it's disabled in opera://plugins. Or, "Proprietary media types" in opera://flags got disabled. Not sure.
Windows Media Player on Windows can handle rtsp.